Field sprayers, as known in the art, are typically attached to, or towed, by an agricultural implement such as a tractor or other vehicle or are a dedicated self-propelled sprayer vehicle. Such sprayers generally include a fluid holding tank supported by a frame. The fluid holding tank typically stores a crop protection fluid, such as pesticides or liquid fertilizer, which often consists of a carrier fluid (such as water) mixed with a chemical at a predetermined concentration. The fluid holding tank, in turn, is fluidly coupled to a series of spray nozzles spaced apart from one another along booms extending outwardly from the frame. Accordingly, the crop protection fluid may be dispensed through the spray nozzles onto the farm field, preferably in an even distribution spray pattern, so that the fluid is applied consistently across the farm field.
In some situations, it may be necessary to meter a flow of liquid material at a very low flow rate, such as on the order of 100 milliliters per minute (mL/min) or less. This situation could arise, for example, while attempting to achieve a low concentration of chemical fluid with respect to a carrier fluid (such as water) to be sprayed. Traditional control techniques, such as reduced nozzle orifice sizes or Pulse Width Modulation (PWM) controlled valves allowing flow only at limited times, have various drawbacks. For example, when operating in agricultural environment in which the soil may be disturbed by movement of the sprayer, particles in the environment or impurities and/or lumps in the chemical fluid may cause very small orifices to clog. Also, most electronically controlled solenoid valves do not respond reliably when the duty cycle of PWM control signals are very low.
What is needed is an improved system for in which a fluid may be reliably metered at very low flow rates.